Will the Firefox recovery key still work if my email address registered with Firefox changes? I don't see an answer to this anywhere yet I see this as very important.
Alle svar (2)
I do not believe so, no. You would still need to be able to access the email address linked to the Firefox Account.
It is quite possible that the recovery key still works as this is about the password of the Sync account, so as long as you do not change the password then the recovery key should still work.
It might be safer to generate a new recovery key if you add a secondary email address and set that as the new primary email. You can't use the recovery key with a new account that has a different email address if that is what you mean as the recovery key is specific to a specific account and password.